Distance finder with automatic range tracking



Jan.'9, 1951 Original Filed July 24, 1942 M. G. CROSBY DISTANCE FINDERWITH AUTOMATIC RANGE TRACKING 2 Sheets-Sheet l a? a g 1| 7 I r 117 10663 s E Moro/r Pawn? l 4' +5 u on 1 3 T C'o/vmousa er E DIFFE/PiA/T/AL i057: l oL-mqs I 105 G3 m7 L. 1/? Bus: fill/F79? 4 wms AL C.

" 19 ?EvERs/ms Moral? INV ENTOR Mae/MY (Roux ATTORNEY 1951 M. G. CROSBY2,537,574-

DISTANCE FINDER WITH AUTOMATIC RANGE TRACKING Original Filed July 24,1942 2 Sheets-Sheet 2 AMPLIFIER Sascm: 6 F/L 75/? E Pmss SHIFTE'? NOISE2'1 3 400% lF/El? JsLEcr/vs INVENTOR M0004) E058) ATTORNEY Patented Jan.9, 1951 DISTANCE FINDER WITH AUTOMATIC RANGE TRACKING Murray G. Crosby,Montclair, N. J., assignor to Radio Corporation of America, acorporation of Delaware Continuation of application Serial No. 452,189,July 24, 1942. This application September 19, 1947, Serial No. 775,029

6 Claims.. (Cl. 343-12) This application is a continuation of myapplication Serial No. 452,189, filed July 24,1942, and entitledDistance Finder. The said application Serial No. 452,189, was abandonedon or about October 20, 1947.

This invention relates to distance finders, and especially to a distancedetermining device in which waves are propagated over direct andindirect paths in which the difference in path length is indicated as afunction of the phase shift of the wave traveling over the indirectpath.

For an understanding of a known type of distance finder, reference isherein made to my United States Patent 2,268,643, granted January 6,1942, which describes one form of distance finder suitable for use inmany systems. The present invention, however, possesses certainadvantages, thus making it a preferred system in many cases.

Briefly stated, the present invention involves transmitting by radiationor otherwise a wave toward the object whose distance is to bedetermined, and receiving the echo or reflected wave in the vicinity ofthe transmitting source after it has been reflected from the object orsurface. The directly transmitted and the reflected waves are thencombined and the combined energy is used to operate an automatic phasecontrol system in such ma nner as to maintain the two waves in a fixedphase relation by varying a phase shifter in one of the paths. The phaseshifter is advanced as the distance between the transmitter and theobject increases, and a calibrated enables a direct reading'of thedistance in suitable units.

The following is a more detailed description of the invention inconjunction with a drawing, wherein Figs. 1 and 2 illustrateschematically two different circuit embodiments of the presentinvention.

The circuit of Fig. 1 shows a specific embodiment in which the distancebetween an object or surface andthe apparatus to the left of it is to bedetermined. A constant radio frequency oscillator I00, of the electrondischarge device type, supplies wave energy to a vacuum tube amplifierIOI through a transformer H5 and also supplies the same wave energythrough lead I I1 to a potentiometer II 3, from which this energy isapplied to the injector grids G3 of a pair of electron discharge devicesI06 and I01. Devicesl06 and I01 are vacuum tubes arranged to function asphase detectors. The output of the energy am-' plifled in vacuum tube I0| is radiated from a suit- .dial mounted on the shaft of the phaseshifter able antenna I02. This radiated energy is directed toward theobject O and the energy reflected by the object O is picked up on asuitable antenna I03, and amplified by a vacuum tube amplifier I04.Amplifier I04 is illustrative of any singlestage or multi-stageamplifier device, preferably provided with an automatic volume controlarrangement. The amplifier I04 feeds the reflected energy to a phaseshifter I05, from which the energy is supplied to the control grids GIof the phase detectors I06, I01 by way of a push-pull transformer H6. Itis preferred that the phase shifter be of the type described in myUnited States Patent 2,247,941, granted July 1, 1941.

Tubes I06 and I01 are, in effect, multi-grid detectors which act asphase detectors to detect the difference in phase between the energyreceived directly from source I00 over lead H1, and the energy radiatedto and reflected from the object 0. It should be noted that the energysupplied to the control grids GI of tubes I06 and I01 from the phaseshifter I05 are supplied to these control grids out of phase withrespect to each other by virtue of the push-pull input transformer II6,whereas the energy supplied to the injector grids G3 of tubes I06, I01from the potentiometer II3 are supplied to these injector grids in acophasal relation. Energy proportional to the phase difference betweenthe direct path (i. e., via lead 1) and the reflected path (via object0) appears across resistors I06 and I09 in the output circuit of thephase detectors, and this energy is used to control the motor powersupply .unit H0, which feeds power to a reversible motor I I2. When theenergy supplied to the phase detectors I06 and I01 over lead H1 and overinput transformer I I6 are at a phase relation, the detector currents inthe outputs of the two phase detectors I06 and I01 are balanced, and novoltage appears across resistors I08 and I09. In this condition noenergy is supplied to apparatus IIO. When the phase between the twoenergies supplied to the phase detectors I06 and I01 deviates from theaforementioned 90 relation, there will be an unbalance in the currentsappearing across the resistors I08 and I09, as a result of which voltageappears across resistors I08 and I09, which is utilized in motor controlapparatus I I0 to supply energy to a two-winding reversible motor II2 tocause it to rotate.

Apparatus H0, in more detail, consists of a pair of amplifiers arrangedso that when the control voltage supplied thereto by the phase detectorsI06 and I01 goes positive, energy is fed to one of the windings of thereversible motor I I2 to cause the motor to rotate in one direction, andwhen the control voltage goes negative, energy is fed to the otherwinding of the motor 2 to reverse the direction of rotation. Equipmentof the type which may be employed in apparatus I I is described in mycopending application Serial No. 435,624, filed March 21, 1942, nowPatent No. 2,380,948, issued August 7, 1945, entitled Electronic MotorControl," to which reference is made for a more detailed descriptionthereof.

The reversible motor I I2 has a shaft I I8 which drives the phaseshifter I in such direction as to restore the phase of the reflectedenergy applied to input transformer II6 to the 90 relation relative tothe directly applied energy from lead H1, in which condition no voltagewill appear across the resistors I08 and I09. A dial I II is shownmounted on the shaft IIB, this dial being calibrated in distance unitsso that the operator is able to read directly from the dial the distancecorresponding to the extent of rotation of the shaft necessary torestore the 90 phase relation condition between the energies appliedover the two different paths to the phase detectors. The readings on thedial give the distance of the object from the distance finder apparatus.It will thus be seen that when the phase of the direct wave and thephase of the reflected wave as applied to the phase detectors I06 andI01 is at 90, no voltage will appear across resistors I08 and I09, andthe reversible motor I I2 will be statlonary. When, however, the phasebetween the direct wave and the reflected wave as applied to the phasedetectors deviates from the 90 relation, a voltage will appear acrossresistors I06 and I09 and cause one of the amplifiers in H0 to supplyenergy to one of the windings of the reversible motorto cause this motorto rotate and drive the shaft of the phase shifter in such direction asto restore the 90 relation, in which position no voltage will againappear at the output of the detectors I06 and I01. By this process, thephase relation between the direct and reflected waves as they are fed tothe detectors is maintained in fixed relation, and changes occurring dueto variation of the distance between the antennas I02, I03 and theobject O are compensated for by the rotation of the shaft of the phaseshifter I05.

An illustration of one particular application of the invention to themeasurement of the height of an aircraft from the ground will now begiven: Let us assume that the distance finder apparatus of Fig. l ismounted on an airplane, and that this airplane is located on the ground,and that the ground corresponds to the object 0. Under this condition,there will be no phase lag due to the reflected wave, and the phaseshifter I05 will automatically rotate to the 90 position to form abalance of the detector anode currents. No voltage will therefore appearacross resistors I08 and I09 at this time. This 90 position should inthis particular illustration be calibrated at zero altitude on the dialIII of the phase shifter. When the airplane leaves the ground, therewill be a certain altitude between the plane and the ground, for-whichreason there will now be a phase lag in the reflected wave and the phaseshifter will automatically advance to compensate for this phase lag.This advance in phase shift caused by a rotation of the shaft I I8 iscalibrated in distance units on the dial III. Inasmuch as the automaticphase control will automatically follow the phase lag introduced by thereflected wave, the dial III will give a constant indication of thealtitude. The phase shifter I05 need be Iii flected waves as applied tothe detectors 206 andcapable of giving no more than 360 shift or, ifdesired, a shift longer than 360. If the phase shifter has a shift of360, it should be provided with a revolution counter on the shaft, or ageared-down dial so that an altitude equivalent to a shift greater than360 (which requires more than one rotation of the shaft II8) will bemeasurable.

In employing a system of the type shown in Fig. l, in actual practice,antennas I02 and I03 will be of the unidirectional type, and so orientedor designed that direct radiation between these two antennas will beprevented.

Another embodiment of the invention is shown 'in Fig. 2 showing acircuit which is designed for audio frequency operation. Instead of anoscillator radiating energy to be reflected back, as shown in Fig. 1,there is employed in Fig. 2 a source of noise 2 I4. This noise source 2I4 may be the inherent noise of the motor of an airplane if the distancefinder apparatus is located on an airplane, or maybe the inherent noiseof the propellers of a vessel if the distance finder is located on avessel. The direct wave is applied by means of microphone 200 and leads2 I5 to an amplifier and selective filter apparatus 202, the output ofwhich feeds the direct wave to the differential vacuum tube phasedetectors 206 and 201 by way of a push-pull audio frequency transformer204. The noise sent out by the source 2 I4 toward the object 0, whosedistance is to be determined, is reflected from the object and picked upby microphone 20 I, which feeds the reflected energy via amplifier andselective filter 203 and through phase shifter 2I0 to the transformer205 of the differential detectors. Fitlers 202 and 203 aid in rejectingsounds other than those emanating from noise source 2 and also serve toselect a given frequency of operation from the noise source. From theforegoing, it will be seen that the reflected wave energy is supplied tothe detectors 206 and 201 in a cophasal relation, while the'direct waveis supplied to the detectors 206 and 201 in an out of phase relation.

In practice, microphone 20I would be a unidirectional type so orientedthat it would not pick up energy directly from the noise source, thusrestricting the energy impinging on this microphone to that reflectedfrom the object. When the direct and reflected waves applied to thephase detectors 206 and 201 are at a phase relation, there will be abalance in the currents in the outputs of the detectors and no voltagewill appear across the resistors 208 and 209. When the phase between thetwo waves applied to the detectors 206 and 201 deviates from the 90relation, a voltage will appear across resistors 208 and 209 of a senseand magnitude corresponding to the direction of deviation and the extentthereof. A relay 2| I has its winding connected across the anodeterminals or resistors 208, 209 as shown. This relay is arranged asillustrated to operate and control a direct current motor 2I2.

Motor 2 I2 has its single field and armature energized by battery 220.Relay 2 serves as a reversing relay for the field voltage and as anonofi relay for the armature voltage. The motor is provided with a shaft2! which serves to rotate the phase shifter 2I0. Phase shifter H0 ispreferably of the type described in my United States Patent 2,247,941. Adial 2I3 is mounted on the shaft 2! and is suitably calibrated indistance In the operation of the system of Fig. 2, when the phasedifference betweenthe direct and re- 201 differs from the 90 relation, avoltage ap-' pears across resistors 208 and 209 which will operate relay2 and start motor 2|: in the proper direction to rotate phase shifter210, to compensate for the phase deviation from the-90 position. Thecontacts of relay 2 are arranged so that a positive voltage in its coilwinding starts the motor 2l2 with one polarity on its field, and anegative voltage across its coil winding starts the motor 2| 2 in theopposite direction, due to the reversal of the terminals of the field ofthe motor produced by the change in direction of operation of the relay2| I. When the phase difference between the direct and reflected wavesas applied to the detectors 206 and 201 is 90", no voltage appearsacross the resistors 208 and 209, and the relay 2 is unenergized, inwhich condition the motor ZIZ will be stationary.

Although the system of Fig. 1 has been described with particularreference to the use of a radio frequency wave, the tuned circuitsthereof being tuned to this particular radio frequency, and while thesystem of Fig. 2 has been described particularly in connection with theuse of sound waves, it should be understood that different applicationsof the invention will require different frequencies. Thus, by varyingthe frequency and choosing the type of wave desired for a particularapplication, the number of wavelengths existing in a given distance maybe varied to provide the requiredsensitivity of the indication.Ordinarily, small distances would require a higher frequency than longerdistances.

What is claimed is:

1. A distance determining device including a source of unmodulated sinewaves of substantially unchanging frequency, a phase detector forcomparing the phase of sine waves, said phase detector having an inputcircuit and an output circuit, a circuit for feeding the input circuitof said detector over one path with unmodulated waves received directlyfrom said source, a wave directive structure for radiating theunmodulated waves produced by said source, a wave directive receivingstructure for receiving the waves radiated by said first structure andreflected back from the object whose distance is to be determined, and acircuit coupled to said wave directive receiving structure for feedingthe input circuit of said detector over another path with waves of thesame frequency as those received on the receiving structure, anadjustable phase shifter in one of said paths, and means for controllingthe adjustment of said phase shifter in response to the energy in theoutput circuit of said phase detector.

2. A distance determining device including a source of unmodulated sinewaves of substantially unchanging frequency, a phase detector forcomparing the phase of sine waves, a circuit for feeding said detectorover one path with unmodulated waves received directly from said source,a

'wave directive structure for radiating the unmodulated waves producedby said source, a wave directive receiving structure for receiving thewaves radiated by said first structure and re fiected back from theobject whose distance is to be determined, and a circuit coupled to saidwave directive receiving structure for feeding said detector overanother path with waves of the same frequency as those received on thereceiving structure, a phase shifter in one of said paths, a reversiblemotor having a shaft linked to said phase shifter for adjusting thephase of the energy passing through said shifter, and means 6 coupled toand deriving energy from said phase detector and responsive to currentsflowing in said phase detector for controlling the movement of saidmotor inaccordance with the polarity of the voltage available in theoutput of said detector.

3. A distance determining device including an electron discharge deviceoscillator producing unmodulated sine waves of substantially unchangingfrequency, an antenna for radiating the waves produced by saidoscillator, a phase detector for comparing the phase of sine waves, saidphase detector having an input circuit and an output circuit, a circuitfor directly supplying the input circuit of said detector withunmodulated waves produced by said oscillator, a pick-up device forreceiving the unmodulated waves radiated from said antenna and reflectedback from the object whose distance is to be determined, a circuitincluding a phase shifter extending from said pickup device to the inputcircuit of said phase detector for supplying said phase detector withunmodulated waves of the same frequency as those received on saidpick-up device, rotatable means in the output circuit of said detectorfor adjusting said phase shifter in response to a voltage appearing insaid output circuit, and an indicator operative with movement of saidphase shifter. I

4. In a distance finder, a source of unmodulated sine waves ofsubstantially unchanging frequency, a phase detector for comparing thephase of sine waves comprising a pair of electron discharge devices, acircuit for supplying a pair of electrodes of said devices in cophasalrelation to each other with an unmodulated sine wave voltage from saidsource, a 'circuit for supplying a pair of electrodes of said devices inout-ofphase relation to each other with another sine wave voltagerepresentative of an unmodulated sine wave reflected from an object orsurface whose distance is to be determined, an adjustable phase shifterin one of said circuits, and means responsive to a voltage developed insaid detector for automatically controlling the adjustment of said phaseshifter to maintain a desired phase relation between said two voltages.

5. In a distance finder, a source of unmodulated sine waves ofsubstantially unchanging frequency, a phase detector for comparing thephase of sine waves comprising a pair of electron discharged devices, acircuit for supplying a pair of control electrodes of said devices incophasal relation to each other with an unmodulated sine wave voltagefrom said source, a circuit for supplying another pair of controlelectrodes of said devices in out-of-phase relation to each other withanother sine wave voltage representative of an unmodulated sine wavereflected from an object or surface whose distance is to be determined,an adjustable phase shifter in one of said circuits, and meansresponsive to a voltage developed in said detector for controlling theadjustment of said phase shifter to maintain a desired phase relationbetween said two voltges.

6. In a distance finder, a source of unmodulated sine waves ofsubstantially unchanging frequency, a phase detector for comparing thephase of sine waves, said phase detector comprising a pair of electrondischarge devices each having a control electrode and an outputelectrode, a circuit for supplying said control electrodes of saiddevices in out-of-phase relation to each other with an unmodulated sinewave voltage from said source, a circuit for supplying the same controlelectrodes of said devices in cophasal relation to each other withanother unmodulated sine wave voltage representative of a wave reflectedfrom an object or surface whose distance is to be determined, anadjustable phase shifter in said last circuit, and means including amotor responsive to a voltage developed across the output electrodes ofsaid detector for controlling the adjustment of said phase shifter tomaintain a desired phase relation between said two voltages.

MURRAY G. CROSBY.

REFERENCES CITED The following references are of record in the file ofthis patent:

8 UNITED s'm'ms PATENTS Number Name Date Jenkins Apr. 29, 1930 HolmesApr. 23, 1940 Strobel July 8, 1941 Guanella Aug. 26, 1941 Green et a1Apr. 4, 1944 Graham July 16, 1946 Isbister Jan. 21, 1947 Bond June 10,1947 Barrow et a1 Sept. 6, 1949

